1. Field of the Invention
The invention relates to an apparatus and a method for the mechanical comminution of semiconductor materials into predetermined size classes.
2. Background Art
Pure silicon is obtained by thermal cracking of silicon compounds, such as for example trichlorosilane, and often takes the form of polycrystalline ingots. To produce single crystals using the Czochralski process, the crystal ingots first of all have to be comminuted into fragments. The fragments are placed in a crucible, with an optimum crucible filling level of molten silicon achieved by use of a combination of different fragment sizes. Then, a seed crystal is used to pull a single crystal from the melt. For the production of polycrystalline solar cells, it is also necessary for the crystal ingots to be comminuted into fragments. These fragments are then cast to form blocks, cut into panels, and processed to form solar cells.
A number of methods for the comminution of silicon ingots have already been proposed. DE 4316626 A1 relates to a comminution method in which a high-pressure water jet is blasted onto a crystal ingot. U.S. Pat. No. 6,360,755 B1 describes a method in which a crystal ingot is comminuted with the aid of shockwaves generated by electrical energy. In DE 3811091 A1, it is proposed that a crystal ingot initially be decompacted by the action of heat and then be comminuted by the action of mechanical force. These comminution methods have the drawback that the size and weight distributions of the majority of the fragments cannot be set in a targeted manner.
A further drawback of conventional comminution machines, such as for example jaw crushers, is the formation of shell-like fragments with a relatively large surface area, and the resulting increase in impurity levels. To avoid these drawbacks, the majority of the polycrystalline silicon ingots are comminuted using manual tools, such as for example hammers. Although this manual method is able to produce the best shape of fragments with very low levels of contamination combined with a good yield, it is physically very hard work.